1. Field of the Invention
The present invention relates to a measurement apparatus, an exposure apparatus, and a device fabrication method.
2. Description of the Related Art
An exposure apparatus which projects and transfers the pattern of a reticle (mask) onto a substrate such as a wafer via a projection optical system is employed to fabricate a semiconductor device using a photolithography technique. The exposure apparatus repeats pattern transfer while changing the shot region on the substrate by moving a stage which holds the substrate. Therefore, to precisely transfer the pattern of the reticle to each shot region on the substrate, it is necessary to accurately position the stage which holds the substrate. Japanese Patent Laid-Open No. 7-270122, No. 6-341861, and No. 2009-33165 propose techniques related to positioning the stage.
Japanese Patent Laid-Open No. 7-270122 proposes a technique of measuring the position of the stage using the interference principle of a diffraction grating. Japanese Patent Laid-Open No. 6-341861 proposes a technique of simultaneously measuring displacements of the stage in two axial directions using, for example, an optical displacement sensor. Japanese Patent Laid-Open No. 2009-33165 proposes a technique of measuring the position of the stage using an interferometer and the interference principle of a diffraction grating together.
Unfortunately, in the related art techniques, measurement errors occur upon measurement of the position of the stage due, for example, to a drawing error resulting from factors associated with drawing of indices on a diffraction grating or a mounting error resulting from factors associated with mounting of the diffraction grating. Measurement errors also occur upon measurement of the position of the stage due, for example, to a change in temperature distribution of a diffraction grating or strain of the diffraction grating with time.